The present invention is directed to the dyeing of foods, such as fruits and vegetables, with oxidation-sensitive water soluble, plant extract natural colors such as betalaine and anthocyanin pigments.
Maraschino cherries have been produced from sweet cherries for an extended period of time. Traditionally, the sweet cherries have been brined in an aqueous SO.sub.2 media, with the SO.sub.2 present in levels above 3,000 ppm. The high SO.sub.2 levels in the cherries allow the cherries to be bacteriostatically stored for months or even years until further processing. Furthermore, while the cherries, when freshly harvested, are heterogeneously colored by their natural occurring anthocyanin pigments, the aqueous SO.sub.2 brine bleaches the fruit to a homogeneous straw-yellow color, and in this condition, the fruit may then be colored by a natural or artificial color to a uniform color shade. In processing, the SO.sub.2 levels are generally lowered to the range of 100-200 ppm by leaching the fruit in fresh water.
Prior art then cooked the cherries at relatively low temperatures for several days in a sugar solution, with the cooking heat improving the diffusion of the sugar into the cherry, while raising the soluble solids level of the solution by dessication of water. During this period of time, the sugar content of the cherry will pass from about 5 to 40% by weight.
During the sugaring process, the SO.sub.2 level in the cherries is generally further reduced, to about 50 ppm or less. Final SO.sub.2 levels of about 10 ppm are not unusual in the finished cherry.
To date, the prior art has normally added a synthetic color during the cooking period, or at least a portion thereof, and the synthetic color is subjected to the cooking temperatures, which are normally in the range of 140.degree. F. to 180.degree. F., for at least one day, in order to diffuse the color into the cherry. Thereafter the cherries are packed in glass containers with the desired syrup added thereto.
The naturally occurring anthocyanin pigment in cherries is oxidation-sensitive, and fades rapidly, imparting to the cherries a brownish appearance, when subjected to oxidation conditions after the cherries are picked. For this reason, it has normally been considered necessary to remove the natural cherry color and replace same with other colors imparting a bright red appearance to the cherries.
Other plant extract, natural colors, such as those derived from other fruits and vegetables, such as, for instance, betalaines from beets, or anthocyanins from grapes, strawberries, cranberries and the like are also generally very sensitive and unstable, with degradation caused by oxygen, heat, metal ions, enzymes and various other factors.
Processes for preparing maraschine cherries or a maraschino style cranberry are disclosed in U.S. Pat. Nos. 2,019,030 to Tucker, 2,494,258 to Nickol and 2,692,831 to Weckel. In the Weckel process of producing a maraschino style cranberry, a hypobaric processing step is used wherein a gas is evacuated from the cranberries without volumetric replacement of the gas by water or other fluid, in order to shrivel the berry skins to densify the cranberries relative to the water in which they are floating, causing them to sink. In this regard, it is clear that complete immersion of the cranberries facilitates a rapid diffusion of sugars and dyes into the berries in subsequent processing steps.
The Tucker process is directed to a secondary bleach step to remove any remaining blemishes from the surface of the cherries after a primary bleach (SO.sub.2) treatment. The Tucker disclosure merely indicates that conventional coloring and syruping steps are utilized with the bleached cherries placed in suspension in a dilute sugar solution containing the proper amount of coloring matter, and presumably thereafter the cherries are subjected to conventional syruping or cooking temperatures. No specific coloring agent is disclosed in this patent.
The Nickol patent discloses a process wherein the syruping of the cherries is effected simultaneously with a removal of sulfur dioxide step. The patent indicates that after the syruping step is completed, additional flavor and color may be added to the syrup, the cooked cherries can be filled into bottles and covered with such syrup, and then pasteurized at 170.degree. F. The Nickol patent does not indicate what coloring agents are utilized and there is no suggestion of maintaining the container contents at low temperatures after color addition, or of avoiding exposure to oxygen (air).
In 1976, the U.S. Food and Drug Administration banned the use of the artificial food coloring agent FD&C Red #4 in foods. Previously this coloring agent had been used to give maraschino cherries their distinctive red color.
The remaining synthetic colors available for coloring the maraschino cherries, FD&C Red #3 and Red #40 are less desirable. FD&C Red #3 is insoluble in water below pH 4, and is subject to color fading upon exposure to light, or upon exposure to SO.sub.2. FD&C Red #40 becomes orange when exposed to SO.sub.2, dulls and darkens upon exposure to light, and fades upon prolonged light exposure. Neither of these dyes adequately covers surface blemishes of dyed fruits. At the present time, FD&C Red #40 is under scrutiny by the FDA as a possible carcinogen, and is not permitted to be used in foods in Canada.
The publication "Food Technology", July, 1977 issue, at page 106, indicates that scientists at Michigan State University were seeking new ways to color maraschino cherries with natural colors. The investigator found that carotenoids were unstable and rapidly oxidized. Beet pigments were examined but reportedly did not work in the pH range which was normally found in cherries, and also had flavor and odor overtones. The anthocyanins were found to be the most promising candidate for a maraschino cherry color, being water soluble and rapidly diffusable into the cherry tissues. The anthocyanins investigated were those in cranberry juice, grape skins, elderberries and purple plums, and cherries were colored with "varying degrees of success".
Beets have previously been used to color pickled eggs, as disclosed in Women's Day Encyclopedia of Cookery, Third Edition, page 66, Fawcett (1966), wherein skinned small young beets are placed in a deep bowl in a solution which also contains hard cooked shelled eggs. The ingredients in the deep bowl are stored in a refrigerator for several days before serving.
It appears that the refrigeration is required because of the chemical instability in air of extracted beet pigments, which otherwise would be subjected to rapid oxidation to a clear or brown state. With adequate refrigeration, however, natural pigments can retain their color for extended periods of time in air.